In situations where balanced signals are created, such as, for example, as shown in the above-identified patent applications, it is sometimes necessary to calculate the phase between two sources. FIG. 2 shows the uncorrected phase (graph 201) of one output relative to the other. Thus, at a phase setting of 45° (point 202), the phase difference between the signals is slightly over 7°, while at a phase setting of 90° (point 203) the phase differences is 1° in the opposite direction. At approximately 180° (point 204) the signals are in phase. Thus, there maybe any arbitrary amount of phase offset between the signals. The phase offset, and phase error, can result in measurement errors. For example, a common mode signal will appear on a differential mode measurement.
FIG. 3 shows the result of correcting the phase, where the phase correction resolution is 1°. The original phase relationship is shown as 201. As expected, the resulting phase output 301 is corrected to less than 1° (½° on either side of zero).
One solution to the problem of error in differential (balanced) drives is to measure the phase deviation and create a correction function to program into a vector modulator such that the correct phase is created for the desired phase setting. The phase of signals is easily measured for continuous wave (CW) signals, but if the signals are modulated, the phase of one relative to the other is difficult to measure. In this case, a second method may be used to establish the phase relationship. In this second method, the differential outputs are combined, and the resulting signal is measured on a signal analyzer or power meter. The phase setting is modified until a minimum signal is obtained. This minimum signal is mapped to phase output of 180°. Other phases may be obtained by programming a differential phase number into the vector modulator used to create the phase difference of the two outputs.